a(n)=a(n-2)+64*a(n-3) with a(0)=1, a(1)=4, a(3)=16.

Terms

a(0) =1a(1) =4a(2) =16a(3) =68a(4) =272a(5) =1092a(6) =4624a(7) =18500a(8) =74512a(9) =314436a(10) =1258512a(11) =5083204a(12) =21382416a(13) =85627972a(14) =346707472a(15) =1454102596a(16) =5826897680a(17) =23643380804a(18) =98889463824a(19) =396564832324